AbstractID: 7781 Title: Direct Optimization of Segments For Intensity-Modulated Radiotherapy
The outputs of inverse planning in conventional intensity-modulated radiotherapy (IMRT) are beams’ intensity maps after an
extremely long optimization progress. Then these intensity maps have to be divided into small segments with uniform intensity if
step-and-shoot delivery technique is to be adopted. This procedure may be not practical because of a long optimization time and
a long time to deliver too many static segments. In this paper a new technique referred as direct optimization of segments (DOS)
is presented. DOS combines the above two steps together. The parameters to be optimized are the number, shape and weight of
segments at all specified beam orientations. Given the maximum segment number of one orientation, the optimization will be
implemented adaptively using our recently developed problem-dependent simulated annealing (PDSA) algorithm. Normally,
20~30 is enough for the maximum segment number of one treatment. In practice, some orientations maybe need more segments,
whereas two or three segments maybe enough for some other orientations. Some practical examples are used to test the efficiency
of the presented DOS technique. The results show the two advantages of DOS. I.e. (1) the optimization is far faster than
pencil-beam-based optimization, because the number of optimized parameters in DOS is less than the pencil-beam number. (2)
There is no doubt that a shorter delivery time will be achieved because of the less number of segments from DOS than that from
conventional IMRT by sequencing of intensity maps.